Traffic and travel information is significant in calculating journey times, and avoiding congestion that delays individual route completion. There are a number of ways of obtaining traffic information and calculating travel time.
In the simplest form travel time is calculated mathematically by dividing the distance to be traveled (either estimated or taken from a map) by the average travel speed (either estimated or taken from an analysis of tachograph data in the case of heavy goods vehicles). Journey time and estimated time of arrival are not particularly accurate, and there is no real consideration of potential traffic congestion of either a long-term nature (for example, road works) or a short-term nature (for example, traffic accidents).
Commercial operations require a greater degree of accuracy to forecast travel times, particularly when using vehicle routing and scheduling techniques to plan vehicle journeys. As a result, traffic planners may use estimated speeds for different types of vehicles over different types of roads (for example, motorways, urban dual carriageways or road surge carriageway arterial roads). Computer based maps with algorithms which determine the shortest path between two points subsequently divides the route into road lengths by type of road and applies estimated speeds to obtain a journey time. Further developments of this technique have, where traffic congestion is known to occur, applied congestion parameters in the form of percentage achievement of the estimated journey time between specific times of the day for particular types of road (for example, urban motorways between 07.30 am and 10.00 am should be 60% of the estimated journey time). However, commercial operators who undertake comparisons of “planned” and “actual” journey times from the tachograph analysis still show significant differences, which are retrospectively found to be caused by traffic congestion.
Traffic congestion at the same location and same time, which is repeated either on consecutive days of the week or the same day of the week, is by its nature forecastable and can be accounted for in traffic planning. However, forecasting based on such repeated congestion does not take account of unpredictable congestion, and thus does not accurately relate the speed of a vehicle to an actual road length at a specific time of day.
Real time traffic information is also required by both drivers and commercial vehicle operators in order to avoid delays caused by unforecastable events such as traffic accidents. There are a number of different ways in which real time traffic information is obtained. The most reliable real time traffic information system is the “incident spotter,” which may be a designated traffic incident reporter (for example, an Automobile Association traffic reporter on a motorbike) reporting traffic congestion to a central control, or a member of the general public (a driver located in traffic congestion) reporting incidents to a radio station by mobile telephone. Local radio stations may consolidate local traffic data from incident spotters, taxi firms, bus companies and the general public to enable them to broadcast real-time traffic information. Such information is normally vetted by means of many reports on the same incident then disseminated to the public by such means as traffic reports on the radio or by means of traffic information reports by cellular telephones. Such a system only reports incidents as they occur and the information is limited to the immediate vicinity of the incident. In addition the radio reports often continue to be broadcast long after the incident is cleared and traffic is proceeding normally because there is often no real verification process after the initial reports. Users may, based upon the information given, make their own informed choice to divert to an alternative route even when it may not be necessary to do so.
More accurate real-time systems use detectors, which are either sensors on road and bridges or cameras alongside the road that are linked to a local traffic reporting (or control) facility, thereby allowing the dissemination of real-time traffic information. Such detectors are normally located at potential traffic congestion points in order that early warning may be issued by the traffic control authority. Such information is often validated by the police or “incident spotters” and passed on to radio stations or organizations providing traffic information by means of cellular telephones. These systems tend to be geographically limited and again, information on an incident may be communicated well after it is cleared and traffic proceeding normally-unless there is a verification procedure which up-dates the situation on a regular basis.
Vehicles fitted with radio data systems with traffic messaging channels (RDS-TMC systems) may also obtain local messaging and be able to process alternative routes through the vehicle navigation system, but this generally only occurs when the original route is either “closed” or “severely delayed”.
A further traffic information system currently available is a network based vehicle tracking and tracing system, which tracks off call handovers of cellulur mobile devices carried in vehicles. As is well known, cellular communication networks track the location of mobile communication devices even when they are not making a call, and keep an up to date record of which location area each mobile device is located in. Generally, each location area is a group of cellular network cells. These records are available from cellular communication network operators and can be used to track the handovers of mobile devices between different location areas. It is well understood how these off call handovers can be used to determine the positions of vehicles at different times and so measure the speed of vehicles passing through location areas. The location areas are relatively large so that the resulting traffic information is of limited use because it is has poor resolution.
A further traffic information system currently available is the individual vehicle tracking and tracing system, which uses a vehicle probe fitted with a global positioning system (GPS) to detect the vehicle location. The vehicle's speed is determined based upon a number of location readings over time. In addition, the vehicle probe has a memory device which records time, data, location and speed at specific time intervals. The collection of such information, either in real-time using a cellular mobile telephone system (GSM) or GPRS, or after the event by radio data download, is known as the “floating vehicle data” (FVD™) technique. This data is both specific and customized to particular vehicles (operated by those requiring the traffic data), and timely insofar as the data can be collected either in real-time or historically. The extensive data may be analysed by type of vehicle, location (road, length), time of day and day of the week. In principle systems of this type can provide very accurate and timely information. However, in practice there can be problems that if the number or density of probe vehicles in a region of the road network is low there may not be sufficient information available to reliably determine traffic conditions.